1. Field of the Invention
The present invention relates generally to electronic pressure measurement devices and, more specifically, to a miniature valve system that includes an integral pressure transducer.
2. Description of the Related Art
A pressure transducer is a device that produces an electric signal in response to a pressure of a gas or liquid. Following the general trend toward miniaturization of electronic components, pressure measurement devices have been produced that include the transducer itself plus associated electronic components needed to produce a useful output signal co-fabricated on a monolithic integrated circuit chip. Such a pressure measurement device is a type of microelectromechanical structure (MEMS). MEMS technology involves producing integrated micro devices or systems that combine electronic components formed on the semiconductor substrate and three-dimensional mechanical components fabricated in the substrate. Sensors and actuators are the primary categories of MEMS devices that have been developed and can range in size from micrometers to millimeters. MEMS devices are fabricated using integrated circuit (IC) lithographic processing as well as micromachining. Micromachining processes include mask-based wet and dry etching and maskless processes such as focused ion beam etching (FIB), laser machining, ultrasonic drilling, and electrochemical discharge machining (EDM) that produce high aspect-ratio features in the substrate.
Examples of MEMS pressure measurement devices are disclosed in M. Schuenemann, et al., "A Highly Flexible Design and Production Framework for Modularized Microelectromechanical Systems," Micromachine Devices, Vol. 3, March 1998. One such device integrates signal processing, a microcontroller, nonvolatile memory and a bus interface, and is packaged in a co-fired ceramic box with top and bottom ball-grid array contacts. MEMS pressure measurement devices of the type disclosed by Schuenemann et al. are not well-suited for installation in small, confined spaces and through apertures because their packages are relatively large.
U.S. Pat. No. 4,695,823, issued to Vernon, suggests incorporating an apparently unpackaged integrated circuit-based pressure transducer in an automotive tire valve. The integrated circuit includes a transmitter that telemeters measured pressure to a remote display unit. The integrated circuit chip is presumably connected to other circuit elements in the conventional manner of an integrated circuit, i.e., by bonding extremely fine wires between microscopic pads on the chip. Such an arrangement would be impractical because fine wires are likely to break under the stresses to which tires and their valves are typically subjected. Moreover, a pressure transducer chip mounted inside a tire valve in any manner similar to that in which an integrated circuit chip is conventionally mounted in a circuit package would similarly subject the chip to stresses to which the chip would respond by producing erroneous output.
It would be desirable to provide an electronic pressure measurement device that can be economically manufactured and included in, for example, an automotive tire valve with minimal likelihood of failure under normal operating conditions and with minimal deviation from industry tire valve standards. These problems and deficiencies are addressed by the present invention in the manner described below.